1. Field of Invention
The present invention relates to a light emitting apparatus. More particularly, the present invention relates to a light emitting apparatus capable of improving output light efficiency, for example, a green light emitting apparatus.
2. Description of Related Art
Recently, solid organic and inorganic light emitting devices, for example, the devices for generating light source, are widely applied. However, the light output efficiency of the light emitting device is one of the important parameters determining the quality thereof. For an inorganic solid light source, for example, GaN based light emitting diode (LED) has the luminescent material such as AlGaInN or InGaN. In general, the light emitting wavelength range of the solid inorganic LED is between 400 nm and 600 nm. However, when the wavelength range is between 525 nm and 575 nm (green light), the light emitting efficiency is sharply reduced. Therefore, the output light emitting efficiency of the conventional inorganic green light LED without luminescent powder is quite low.
In order to have higher green output light emitting efficiency, in the conventional manner, inorganic UV LED or inorganic blue LED is used to excite high efficient green light luminescent powder to generate green light. FIG. 1 is a schematic cross sectional view of the conventional inorganic UV or Blue LED with green luminescent powder. Referring to FIG. 1, a structural body 100 has a conducting wire structure 112, an LED device 105 and an encapsulating body. The conducting wire structure includes, for example, a n pad conducting wire 102 and a p pad conducting wire 104. The LED device 105 is disposed in the encapsulating body of the structural body 100, and electrically coupled with the n pad conducting wire 102 and the p pad conducting wire 104. For example, LED device 105 may emit UV light or blue light under suitable applied voltage. The structure of the conventional inorganic LED device 105 includes at least a n-type semiconductor layer 106, a p-type semiconductor layer 108, and a light emitting active layer between the two semiconductor layers. The p-type semiconductor layer 108 is connected to the p pad conducting wire 104 by an electrode layer 110 and a wire 112. When an operating voltage is applied to the LED device 105, for example, UV light or blue light may be emitted from each direction, as shown by the arrows. Further, an encapsulating layer 114, such as epoxy, fills into the encapsulating body of the structural body 100. The green luminescent powder 116 is distributed over inside the encapsulating body 114.
The UV light or the blue light emitted by the LED 105 can excite the green luminescent powder 116 to generate green light. In single exciting process on the green luminescent powder, the green light conversion is not 100%. The disadvantages of the above-mentioned approaches lie in the facts that are the UV light left uncoverted is not recycled to excite the luminescent powder again and thus is converted into green light, and light absorption loss of UV light or of blue light due to total internal reflection and Fresnel reflection loss is not reduced or eliminated. Therefore, the green light output efficiency becomes seriously low. Further, in order to let the green light emit in a direction range efficiently, a reflector 118 may also be disposed at the inner peripheral of the encapsulating body.
The conventional light emitting apparatus as shown in FIG. 1 may effectively generate green light, but the light extraction efficiency requires further improvement. Currently the manufacturers still continue to develop new technology to improve the output light efficiency.